Does it matter if a film perverts history? No one who really wants to know the truth about the past has ever gone to Hollywood for enlightenment. The epic in particular is a form that likes its conflicts presented in clear-cut black and white, while real historical dramas tend to be full of ambiguity and mixed motivation.

Zack Snyder's new movie, 300, aims to describe the heroic resistance of the 300 Spartan warriors who held the pass at Thermopylae in August 480BC against the invading Persian army. It is - as the blurb claims - "300% action". Instead of boringly detailed reconstruction of battle scenes involving grunting warriors, clashing shields and clanking swords, Snyder's smooth style and "speed-ramping" techniques give us a glidingly panoramic view of the battle that helped "save Greece for democracy". He made his name in music videos - and as an entertainment for the eye, 300 compares well with the two best current contenders in that genre: Take That's dazzling version of their hit single Shine, and the frenetic hedonism of Scissor Sisters gyrating, counter-intuitively, to Don't Feel Like Dancin'.

The film is based on Frank Miller's highly successful graphic novel of the same name. Just like that comic book series of illustrations, it evokes the geographical context of the battle to superb effect. Plot keywords for Snyder include "breasts", "graphic violence" and "beheading" - commodities and acts displayed to prodigal effect on screen. For "breasts" one should read "pecs", since Snyder's warriors come out of the central gym of screen casting. Wearing little more than sandals, cloaks and some form of leather briefs, the 300 members of the Spartan royal guard leap the centuries straight into the illustrated pages of men's magazines advertising the benefits of dietary supplements.

This will annoy the historian who wants truth unvarnished, since the real warriors of 480BC would have worn fairly extensive body armour. They would have been crazy not to, given the murderous efficacy of Persian archery. Still, it would be mean-spirited to deny 300's actors their buffed moments in the sun, having endured so many months of training. It's when their mouths open, however, that the film falls apart and becomes an American corporation's viciously misleading view of history - both ancient and contemporary.

The Warner Brothers' view of the Greco-Persian wars takes its cue from the 5th century Greeks - especially the Athenians - who saw it as a conflict between liberty and tyranny. Having been defeated at Marathon 10 years earlier, the Persian army returned to Greece bent on vengeance. There may have been some 20,000 of them, and the 300 Spartans, aided by 1,000 Boeotians, certainly held Xerxes's army for a couple of days at the pass of Thermopylae before succumbing to the superior force.

The delay gave the Greeks some time to prepare defences, and revenge came the following month when fewer than 400 ships lured over 1,000 Persian ones into the bay of Salamis before sinking them. Thermopylae and Salamis were subsequently used by Greek propaganda to show how guts and cleverness could get the better of an enclosed palace society, despite Persia's vastly superior riches and military resources.

Histories written by later European liberals are full of doom-laden sighs about the consequences had the Persians won: no democracy à la Grecque, no philosophy or science, and Euripides might have spent his time composing ditties praising the great king at the Persian court in Persepolis. Snyder's characters mouth George Bush platitudes about "freedom", but Spartans, being the product of a militarised oligarchy, were hardly democratic warriors. The Spartan regime retained kingship and was pathologically philistine: it saw the arts as a dangerous diversion that might undermine the martial energy it had deployed in campaigning against other Greek states.

The Persian threat had united previously quarrelsome Greek city states - just as US intervention in the Middle East has created a vast new force of "friends of al-Qaida". But Snyder's 300 is an uncritical reflection of neocon foreign policy filmed at a time when that crazed ideology was at its most influential. Now it's been released, it looks like a video war-game, and has excited protests in Tehran with its characterisation of ancient Persian warriors as cruel despots. Jake Shears and Gary Barlow seem safer - and nicer - westernising exports than Snyder's hoarse-voiced thugs.

· Hywel Williams's history of kingship, Sun Kings, is published in September by Quercus; 300 opens on Fridaycaradog@btconnect.com